A gas turbine engine which uses an axial (axial-flow) compressor includes a diffuser located downstream of a compressor. An outlet guide vane is provided at an inlet of the diffuser. When the outlet guide vane is supported on the outer wall surface of the diffuser, a gap is often provided between the outlet guide vane and the inner wall surface of the diffuser. To prevent the thermally expanded outlet guide vane from contacting the inner wall surface of the diffuser, the gap is provided between the outlet guide vane and the inner wall surface of the diffuser. In this structure, air leaks through the gap and a pressure loss increases, which may reduce the compressor efficiency. To solve this problem, there is a gas turbine in which a recess is formed in the inner wall surface of the diffuser and the front edge of the outlet guide vane is inserted into the recess to prevent air leakage (e.g., see FIG. 8 in Patent Literature 1).